The present invention generally relates to semiconductor devices and more particularly to a semiconductor package having a single in-line structure.
In order to improve the efficiency for mounting semiconductor devices on a support substrate such as a printed circuit board, a package structure designed for surface mounting technology (SMT) is used extensively. By using surface mounting technology, a semiconductor device can be mounted on the circuit board without providing holes for inserting leads of the device. The soldering of the leads is achieved by merely placing the device on the circuit board and passing the device through a heating furnace for causing a reflowing of the solder alloy. Thereby, the efficiency of the mounting process is improved significantly and the fabrication cost of electronic apparatuses that use the semiconductor devices is significantly reduced.
In order to mount as many as possible of the semiconductor devices on a single support substrate, a single in-line package (SIP) is proposed. In a single in-line package, the leads are provided along a single edge of a flat package body to extend perpendicularly with respect to the edge, and the package body is held upright on the substrate by inserting the leads into corresponding holes in the substrate. As the package body is held vertically on the substrate, the number of packages that may be mounted on the substrate is increased. Further, such a structure is advantageous for cooling the device.
In order to combine the advantageous feature of the single in-line package with the advantageous feature of surface mounting technology, a package structure shown in FIG. 1 is proposed in the U.S. Pat. No. 4,975,763.
Referring to FIG. 1, the package designated by a numeral 1 includes a flat resin package body 2 that accommodates therein a semiconductor chip 3. At an edge 2a of the flat package body 2, there are provided a number of leads 4 having an inner lead part 4a connected to a bonding pad of the chip 3 and an outer lead part 4b extending outward from the edge 2a. Further, the outer lead part 4b of the leads 4 is bent laterally with respect to the extending direction of the leads 4. In order to support the package body 2 on a substrate at the time of mounting, there is provided a pair of studs 5 each including a stop portion 6 and a cylindrical clip portion 7 of a reduced diameter for insertion into a corresponding hole provided on the substrate.
FIG. 2 shows the mounting of the package 1 on a substrate 8, wherein the substrate 8 is formed with a hole 8a for holding the clip portion 7 of the stud 5. The portion 7 is inserted into the hole 8a as shown in FIG. 2 and the package body 2 is held upright on the substrate 8. The substrate 8 carries thereon a conductor pattern 8b for wiring, and the lead 4 is contacted with the conductor pattern 8b when the package 1 is held on the substrate 8. By passing the substrate 8 together with the package 1 in the state shown in FIG. 2 through a heating device, the soldering alloy provided on the conductor pattern 8b is caused to reflow and the lead 4 is soldered firmly upon the conductor pattern 8.
In this conventional package structure, there is a problem in that one has to provide the hole 8a on the substrate 8 in correspondence to the stud 5 for holding the package body 2 on the substrate 8. As each lead 4 has to engage with a corresponding pattern 8b when the package is mounted, it is necessary that the hole 8a be formed with high precision. This requirement is particularly acute in the recent semiconductor devices that have a large number of leads on the package body. Obviously, such a formation of the hole and the insertion of the stud into the hole undermine the advantageous feature of the surface mounting technology, and the efficiency of mounting is inevitably deteriorated.
Meanwhile, there are various semiconductor devices that generate heat upon operation. Thus, there is a need for a semiconductor package that facilitates efficient cooling of the device. The conventional package of FIG. 1 has a drawback with respect to this point in that the package lacks a cooling fin. Thus, the dissipation of the heat has to be achieved via the resin package body. As will be easily understood, such a process of heat dissipation is inefficient and the package structure of FIG. 1 can be used only for those devices that produce little heat. The process for mounting a cooling fin on the resin package body complicates the fabrication process of the device.